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Functional Sn-Bi alloy plating using a substitute material for Pb
6478944 Functional Sn-Bi alloy plating using a substitute material for Pb
Patent Drawings:Drawing: 6478944-2    Drawing: 6478944-3    Drawing: 6478944-4    
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Inventor: Ishiyama
Date Issued: November 12, 2002
Application: 09/566,125
Filed: May 5, 2000
Inventors: Ishiyama; Masaaki (Tokyo, JP)
Assignee: Nishihara Rikoh Corporation (Tokyo, JP)
Primary Examiner: Nguyen; Nam
Assistant Examiner: Nicolas; Wesley A.
Attorney Or Agent: Greenblum & Bernstein, P.L.C.
U.S. Class: 205/102; 205/104; 205/123; 205/252
Field Of Search: 205/252; 205/50; 205/102; 205/253; 205/254; 205/238; 205/104; 205/105; 205/123; 438/106
International Class:
U.S Patent Documents: 5643432; 5674374; 5759379; 5948235
Foreign Patent Documents: 0474499; 63-49382; 2543619; 63187654
Other References: An English Language abstract of JP 63-187654..
An English Language abstract of JP 63-49382..









Abstract: The present invention relates to a to-be-mounted electronic component to which functional alloy plating using a bonding material for mounting is applied with a substitute bonding material for solder (tin-lead alloy), and aims at providing alloy plating which has been put to a practical use in such a way that the function of existing alloy plating of this type has been significantly improved to eliminate toxic plating from various kinds of electronic components for use in electronic devices so that it is useful in protecting the environment.
Claim: What is claimed is:

1. A process for functional alloy plating using substitute bonding material for Pb, comprising applying functional alloy plating to an electronic component to be mounted usingan electrolytic process with a pulse waveform, said functional alloy plating comprising Sn as base, and Bi, wherein said Bi content to said Sn is set to one of 1.0% or less, and 2.0 to 10.0%.

2. The process according to claim 1 wherein the pulse waveform cycles between positive and negative.

3. The process according to claim 2 wherein the pulse waveform cycling between positive and negative comprises a 6-phase half-wave.

4. The process according to claim 3 wherein the 6-phase half wave comprises a thyristor 6-phase half wave.

5. The process according to claim 1 wherein said Bi is set to 1.0% or less.

6. The process according to claim 1 wherein said Bi is set to 2.0 to 10.0%.

7. A process for functional alloy plating using substitute bonding material for Pb, said process comprising wire-bonding an IC chip to a lead frame, and subjecting outer leads exposed outside a molded IC package to an electrolytic process withan Sn content which is 99.0% or greater, and a Bi content to said Sn being set to 1.0% or less and with a pulse waveform.

8. The process according to claim 7 wherein the pulse waveform cycles between positive and negative.

9. The process according to claim 8 wherein the pulse waveform cycling between positive and negative comprises a 6-phase half-wave.

10. The process according to claim 9 wherein the 6-phase half wave comprises a thyristor 6-phase half wave.

11. A process for functional alloy plating using substitute bonding material for Pb, said process comprising wire-bonding an IC chip to a lead frame, and subjecting outer leads exposed outside a molded IC package to an electrolytic process withan Sn content which is 98.0 to 90.0%, and a Bi content to said Sn being set to 2.0 to 10.0% and with a pulse waveform.

12. The process according to claim 11 wherein the pulse waveform cycles between positive and negative.

13. The process according to claim 12 wherein the pulse waveform cycling between positive and negative comprises a 6-phase half-wave.

14. The process according to claim 13 wherein the 6-phase half wave comprises a thyristor 6-phase half wave.

15. A process for functional alloy plating using substitute bonding material for Pb comprising subjecting an electrode pattern of a printed circuit board to an electrolytic process with an Sn content which is 99.0% or greater, and a Bi contentto said Sn being set to 1.0% or less and with a pulse waveform.

16. The process according to claim 15 wherein the pulse waveform cycles between positive and negative.

17. The process according to claim 16 wherein the pulse waveform cycling between positive and negative comprises a 6-phase half-wave.

18. The process according to claim 17 wherein the 6-phase half wave comprises a thyristor 6-phase half wave.

19. A process for functional alloy plating using substitute bonding material for Pb comprising subjecting an electrode pattern of a printed circuit board to an electrolytic process with an Sn content which is 98.0 to 90.0%, and a Bi content tosaid Sn being set to 2.0 to 10.0% and with a pulse waveform.

20. The process according to claim 19 wherein the pulse waveform cycles between positive and negative.

21. The process according to claim 20 wherein the pulse waveform cycling between positive and negative comprises a 6-phase half-wave.

22. The process according to claim 21 wherein the 6-phase half wave comprises a thyristor 6-phase half wave.

23. A process for functional alloy plating using substitute bonding material for Pb comprising wire-bonding a chip tantalum capacitor to a lead frame, and subjecting outer leads exposed outside said chip tantalum capacitor to an electrolyticprocess with an Sn content which is 99.0% or greater, and a Bi content to said Sn being set to 1.0% or less and with a pulse waveform.

24. The process according to claim 23 wherein the pulse waveform cycles between positive and negative.

25. The process according to claim 24 wherein the pulse waveform cycling between positive and negative comprises a 6-phase half-wave.

26. The process according to claim 25 wherein the 6-phase half wave comprises a thyristor 6-phase half wave.

27. process for functional alloy plating using substitute bonding material for Pb comprising wire-bonding a chip tantalum capacitor to a lead frame, and subjecting outer leads exposed outside said chip tantalum capacitor to an electrolyticprocess with an Sn content which is 98.0 to 90.0%, and a Bi content to said Sn being set to 2.0 to 10.0% and with a pulse waveform.

28. The process according to claim 27 wherein the pulse waveform cycles between positive and negative.

29. The process according to claim 28 wherein the pulse waveform cycling between positive and negative comprises a 6-phase half-wave.

30. The process according to claim 29 wherein the 6-phase half wave comprises a thyristor 6-phase half wave.

31. A process for functional alloy plating using substitute bonding material for Pb comprising subjecting general electronic device component materials including a component material which needs plating for bonding and a general componentmaterial which needs plating as a functional component to an electrolytic process with an Sn content which is 99.0% or greater, said Bi content to said Sn being set to 1.0% or less and with a pulse waveform.

32. The process according to claim 31 wherein the pulse waveform cycles between positive and negative.

33. The process according to claim 32 wherein the pulse waveform cycling between positive and negative comprises a 6-phase half-wave.

34. The process according to claim 33 wherein the 6-phase half wave comprises a thyristor 6-phase half wave.

35. A process for functional alloy plating using substitute bonding material for Pb comprising subjecting general electronic device component materials including a component material which needs plating for bonding and a general componentmaterial which needs plating as a functional component to an electrolytic process with an Sn content which is 98.0 to 90.0%, said Bi content to said Sn being set to 2.0 to 10.0% and with a pulse waveform.

36. The process according to claim 35 wherein the pulse waveform cycles between positive and negative.

37. The process according to claim 36 wherein the pulse waveform cycling between positive and negative comprises a 6-phase half-wave.

38. The process according to claim 37 wherein the 6-phase half wave comprises a thyristor 6-phase half wave.
Description: DETAILED DESCRIPTION OF THE INVENTION

Field of Utilization in Industry

The present invention relates to a to-be-mounted electronic component to which functional alloy plating using a bonding material for mounting is applied with a substitute bonding material for solder (tin-lead alloy), and aims at providing alloyplating which has been put to a practical use in such a way that the function of existing alloy plating of this type has been significantly improved to eliminate toxic plating from various kinds of electronic components for use in electronic devices sothat it is useful in protecting the environment.

Background of the Invention

As solder which does not use lead (Pb) (Pb-free solder), various new bonding agents have been developed and their properties become apparent. And, the stage is proceeding to the development of their manufacturing methods. Tin (Sn)-bismuth (Bi),Sn-indium alloy-(In), Sn-zinc alloy (Zn), Sn plating etc. are considered as Pb-free solder to devices. The cost for the Sn--In alloy among them is extremely high, about 25 times the cost for Sn--Bi The Sn--Zn alloy has a problem on the solderabilityafter heat resistance because Zn is prone to be oxidized. This leaves Sn--Ag, Sn--Bi and Sn.

Bi on copper may be thermally diffused at the time of reflow and may be peeled, so that Sn--Bi for devices should have nickel applied as a base in order to avoid the peeling.

If a coat offset (melt-originated offset) occurs when a surface-mounting device is melted, tho bonding surface has a rough surface, so that the bonding surface becomes smaller, thus lowering the bonding strength. Prevention of a melt-originatedoffset which makes organic eutectoid in a coat extremely small is attempted by applying plating according to this invention.

Prior Art

Conventionally, solder (tin-lead alloy) has been used for a long time as a bonding material for mounting electronic device components. Recently, the harmfulness of lead has been noticed mainly in America and Europe and removal of lead fromelectronic devices has progressed rapidly.

Meanwhile, in Japan has already started a movement of voluntary removal mainly by the electronics industry.

Electroplating is applied to most of materials for to-be-mounted electronic components as tinning. Therefore, there is a pressing need to industrialize plating of substitute alloys for the industrial growth.

Problem to be Solved by the Invention

As solder which is an essential bonding material for the aforementioned electronic components contain lead (Pb), however, when electronic devices are disposed of, lead would be melted and seep into groundwater from a junk yard, raising a problemof environmental pollution, unless electronic components having to-be-mounted parts containing solder's lead are removed.

Means for Solving the Problem

Accordingly, it is an object of this invention to overcome the problem of the prior art and to provide electronic components to be on which very practical alloy plating for bonding that is the existing alloy plating of this type which has beenimproved significantly is applied using a substitute metal for lead in solder alloy plating.

The first of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that with Sn as a base, one of Bi, Ag andCu is selected, a Bi content to the Sn is set to 1.0% or less, the Bi content to the Sn is set to 2.0 to 10.0%, an Ag content to the Sn is set to 1.0 to 3.0%, the Ag content to the Sn is set to 3.0 to 5.0%, the Ag content to the Sn is set to 8.0 to10.0%, or a Cu content to the Sn is set to 5 to 1.0%, and an electrolytic process is performed with a special waveform.

The second of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that an IC chip is wire-bonded to a leadframe and outer leads exposed outside a molded IC package are subjected to an electrolytic process with a Bi content to Sn whose content is 99.0% or greater being set to 1.0% or less and with a special waveform.

The third of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that an IC chip is wire-bonded to a leadframe and outer leads exposed outside a molded IC package are subjected to an electrolytic process with a Si content to Sn whose content is 98.0 to 90.0% being set to 2.0 to 10.0% and with a special waveform.

The fourth of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that an IC chip is wire-bonded to a leadframe and outer leads exposed outside a molded IC package are subjected to an electrolytic process with an Ag content to Sn whose content is 99.0 to 97.0% being set to 1.0 to 3.0% and with a special waveform.

The fifth of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that an IC chip is wire-bonded to a leadframe and outer leads exposed outside a molded IC package are subjected to an electrolytic process with an Ag content to Sn whose content is 97.0 to 95.0% being set to 3.0 to 5.0% and with a special waveform.

The sixth of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that an IC chip is wire-bonded to a leadframe and outer leads exposed outside a molded IC package are subjected to an electrolytic process with an Ag content to Sn whose content is 92.0 to 90.0% being set to 8.0 to 10.0% and with a special waveform.

The seventh of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that an IC chip is wire-bonded to a leadframe and outer leads exposed outside a molded IC package are subjected to an electrolytic process with a Cu content to Sn whose content is 99.5 to 99.0% being set to 0.5 to 1.0% and with a special waveform.

The eighth of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that an electrode pattern of a printedcircuit board is subjected to an electrolytic process with a Bi content to Sn whose content is 99.0% or greater being set to 1.0% or less and with a special waveform.

The ninth of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that an electrode pattern of a printedcircuit board is subjected to an electrolytic process with a Bi content to Sn whose content is 98.0 to 90.0% being set to 2.0 to 10.0% and with a special waveform.

The tenth of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that an-electrode pattern of a printedcircuit board is subjected to an electrolytic process with an Ag content to Sn whose content is 99.0 to 97.0% being set to 1.0 to 3.0% and with a special waveform.

The eleventh of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that an electrode pattern of a printedcircuit board is subjected to an electrolytic process with an Ag content to a content of 97.0 to 95.0% being set to 3.0 to 5.0% and with a special waveform.

The twelfth of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that an electrode pattern of a printedcircuit board is subjected to an electrolytic process with an Ag content to a content of 92.0 to 90.0% being set to 8.0 to 10.0% and with a special waveform.

The thirteenth of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that an electrode pattern of a printedcircuit board is subjected to an electrolytic process with a Cu content to Sn whose content is 99.5 to 99.0% being set to 0.5 to 1.0% and with a special waveform.

The fourteenth of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that a chip tantalum capacitor iswire-bonded to a lead frame and outer leads exposed outside the chip tantalum capacitor are subjected to an electrolytic process with a Bi content to Sn whose content is 99.0% or greater being set to 1.0% or less and with a special waveform.

The fifteenth of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that a chip tantalum capacitor iswire-bonded to a lead frame and outer leads exposed outside the chip tantalum capacitor are subjected to an electrolytic process with a Bi content to Sn whose content is 98.0 to 90.0% being set to 2.0 to 10.0% and with a special waveform.

The sixteenth of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that a chip tantalum capacitor iswire-bonded to a lead frame and outer leads exposed outside the chip tantalum capacitor are subjected to an electrolytic process with an Ag content to Sn whose content is 99.0 to 97.0% being set to 1.0 to 3.0% and with a special waveform.

The seventeenth of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that a chip tantalum capacitor iswire-bonded to a lead frame and outer leads exposed outside the chip tantalum capacitor are subjected to an electrolytic process with an Ag content to Sn whose content is 97.0 to 95.0% being set to 3.0 to 5.0% and with a special waveform.

The eighteenth of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that a chip tantalum capacitor iswire-bonded to a lead frame and outer leads exposed outside the chip tantalum capacitor are subjected to an electrolytic process with an Ag content to Sn whose content is 92.0 to 90.0% being set to 8.0 to 10.0% and with a special waveform.

The nineteenth of this invention-is function alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that a chip tantalum capacitor iswire-bonded to a lead frame and outer leads exposed outside the chip tantalum capacitor are subjected to an electrolytic process with a Cu content to Sn whose content is 99.5 to 99.0% being set to 0.5 to 1.0% and with a special waveform.

The twentieth of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that general electronic devicecomponent materials including a component material which needs plating for bonding and a general component material which needs plating as a functional component are subjected to an electrolytic process with a Bi content to Sn whose content is 99.0% orgreater being set to 1.0% or less and with a special waveform.

The twenty-first of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that general electronic devicecomponent materials including a component material which needs plating or bonding and a general component material which needs plating as a functional component are subjected to an electrolytic process with a Bi content to Sn whose content is 98.0 to90.0% being set to 2.0 to 10.0% and with a special waveform.

The twenty-second of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that general electronic devicecomponent materials including a component material which needs plating for bonding and a general component material which needs plating as a functional component are subjected to an electrolytic process with an Ag content to Sn whose content is 99.0 to97.0% being set to 1.0 to 3.0% and with a special waveform.

The twenty-third of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that general electronic devicecomponent materials including a component material which needs plating for bonding and a general component material which needs plating as a functional component are subjected to an electrolytic process with an Ag content to Sn whose content is 97.0 to95.0% being set to 3.0 to 5.0% and with a special waveform.

The twenty-fourth of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that general electronic devicecomponent materials including a component material which needs plating for bonding and a general component material which needs plating as a functional component are subjected to an electrolytic process with an Ag content to Sn whose content is 92.0 to90.0% being set to 8.0 to 10.0% and with a special waveform.

The twenty-fifth of this invention is functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied, characterized in that general electronic devicecomponent materials including a component material which needs plating for bonding and a general component material which needs plating as a functional component are subjected to an electrolytic process with a Cu content to Sn whose content is 99.5 to99.0% being set to 0.5 to 1.0% and with a special waveform.

Embodiment

Significance of Special Waveform

A description will now be given of the aforementioned "electrolytic process with a special waveform". First, typical electroplating is DC plating, i.e., plating with a voltage having an AC voltage rectified by a rectifier.

To perform plating, it is necessary to combine and add several types of organic additives into a plating solution so that the crystal grain size of metal to be deposited does not become resin particle size.

Of course, those organic materials become eutectoid at the same time as the metal to be plated, causing many defects on their functions as bonding materials.

The "electrolytic process with a special waveform" in this invention improves those shortcomings, and an additive to be added into a plating solution is only a slight amount of a surface active agent which is not decomposed and disposed, and thisspecial waveform serves as an organic additive.

In this invention, the special waveform is a pulse waveform which is acquired for an electrolytic process from a current that has been rectified with a thyristor 6-phase half wave. Thus, the electrolytic process uses a pulse waveform which cancycle between positive and negative.

The following shows a table of the types of mass-producible platings.

TABLE 1 Melt- originated Coats Composition offset Note Sn-Ag Ag 10% special .largecircle. Plating by special waveform plating waveform method of this invention Sn-Ag Ag 3% special X Melt-originated offset waveform plating present evenwith plating by special waveform method of this invention Sn-Bi Bi 3% special .largecircle. Plating by special waveform plating waveform method of this invention Sn Sn 100% X Normal gloss plating Sn Sn 99% special .largecircle. Plating by special waveform plating waveform method of this invention Sn-Pb Pb 10% special .largecircle. Plating to which- waveform plating existing chip tantlum is applied

As there are different coat characteristics to be acquired depending on whether the lead types of devices to be used are lead lines, a lead frame or leadless, they should be selectively used, but the added values of the devices differ device bydevice so that a cost-based selection is also considered as an important factor.

In the comparison of the costs for plating materials, the cost for the base acid is high even if an inexpensive metal is used, so that the cost does not decrease as indicated in the comparison of the prices of metals. A further variation is seenwhen it is run as plating.

Then, the following table shows the evaluation of Pb-free coats as coats.

TABLE 2 Types of coats Contents Note Sn-Ag plating Ag 3-10% Melting point of 220-260.degree. C. Melt-originated offset occurred by C, Ag composition. Glossy appearance Sn-bi plating special waveform Melting point of 220-225.degree. C. plating contain- Fragile due to diffusion of ing Bi of 2-5% Bi into C, copper base. Glossless appearance Sn plating Different type Melting point of 225-230.degree. C. of metal of 0.2- Good reflow. Semi-gloss 1% contained as appearance additive

The following table shows a list of the evaluation of the individual coats.

TABLE 3 Sn-Ag Sn-Bi Sn Appearance Gloss Glossless Semi-gloss Plating 4.03 .mu.m 4.21 .mu.m 3.99 .mu.m thickness Composition Sn 92.46% Sn 97.31% Sn 99.8% Ag 7.54% Bi 2.69% Bi 0.16% Heat Discoloration Passed Passed resistance present Solderability Passed Passed Passed after heat resistance Bending after Passed Passed Passed heat resistance Peeling after Passed Passed Passed heat resistance Melt- Present None None originated offset Solder Zero-cross Zero-cross Zero-cross wettability 0.65 sec 0.85 sec 0.50 sec before heat Wet strength Wet strength Wet strength resistance 71.4 mg 23.0 mg 31.4 mg Solder Zero-cross Zero-cross Zero-cross wettability 0.95 sec 0.87 sec 0.61 sec after heat Wet strength Wet strength Wetstrength resistance 26.4 mg 23.0 mg 34.2 mg Bonding 0.37 Kg before 1.56 Kg before 1.63 Kg before strength heat heat heat resistance resistance resistance 0.05 Kg after 0.05 Kg after 0.70 Kg after heat heat heat resistance resistance resistance Vickers 16.3 23.0 11.4 hardness

The following table shows the costs for the individual coats.

TABLE 4 Price of Price in mass- Sample price prototype production (.Yen./Kg) (.Yen./Kg) (.Yen./Kg) Sn-Ag 2,352 2,114 1,685 Sn-Bi 1,488 1,363 1,148 Sn special wave- 1,518 1,518 1,089 form plating Special wave -- -- -- form plating

While the samples shown above had a nickel (Ni) base to avoid diffusion on copper, Sn--Ag showed such a phenomenon that oxidization on Ni through Ag at the time of heat resistance lowered the bondability. In this respect, it is contemplated thatcopper (Cu) is suitable as the base for Sn--Ag. Further, heat-resistance-originated discoloration and melt-originated offset also occurred. To cope with this melt-originated offset, it is necessary to obtain Sn--Ag plating containing 85% or more of Ag,which is naturally a factor to increase the cost. Slight segregation is seen on the surface of Sn--Bi. Sn--Ag and Sn-special waveform plating still suffer poor solution efficiencies and the line speeds remain about a half the speed of the currentspecial-waveform plating. Although solution conditions were so set as to provide the optimal appearance in the implementation of the scheme, improvements can be made on the density of the solution, the density of the additive, stirring and so forth. Inthe case of surface mounting, there may be a question on the behavior of Bi, such as segregation or diffusion. In this respect, Bi in the Sn-special waveform plating has a minute amount and serves to adjust the deposition of the plated coat so that itdoes not seem to raise a problem on segregation or diffusion.

The following gives the results of the evaluation of samples of Sn--Ag, Sn--Bi. and Sn plating to chip tantalum frames.

(1) Plating Specifications base plating Ni 0.5 to 1.0 .mu.m (same for all) finishing plating Sn--Ag 3.0 to 5.0 .mu.m Sn--Bi 3.0 to 5.0 .mu.m Sn 3.0 to 5.0 .mu.m (2) Test Results "Sn--Ag" a. Appearance: passed (free of spot, stain and discoloration) b. Heat resistance: discoloration present (160.degree. C. .times. 6 Hr heat resistance. no expansion, peeling, discoloration and fall-off) c. Solderability test: passed (after heat resistance, 230.degree. C. .times. 3 sec .times.once n = 1) d. Bending test: passed (after heat resistance, 180.degree. C., bend-back test, measured at A n = 1) e. Melt-originated: no melt-originated offset (no heat offset resistance 270.degree. C. .times. 30 min .times. once n = 1) f. Peelingtest: passed (sample before and after heat resistance n = 1) g. Melting point: 222.degree. C. h. Hardness (Vickers hardness): 16.3 i. Solder: zero-cross time before heat resistance wettability average 0.65 (sec) after heat resistance average 0.95(sec) wet strength before heat resistance average 71.40 (mg) after heat resistance average 26.40 (mg) (n = 5) j. Bonding: before heat resistance average 0.37 (kg) strength: after heat resistance average 0.05 (kg) (n = 5) k. Plating thickness:average 4.03 (.mu.m) (measured with fluorescent X rays n = 9) l. Composition: Sn 92.46% Ag 7.54% "Sn--Bi" a. Appearance: passed (free of spot, stain and discoloration) b. Heat resistance: passed (160.degree. C. .times. 6 Hr heat resistance. noexpansion, peeling, discoloration and fall-off) c. Solderability test: passed (after heat resistance, 230.degree. C. .times. 3 sec .times. once n = 1) d Bending test: passed (after heat resistance, 180.degree. C., bend-back test, measured at A n =1) e. Melt-originated: no melt-originated offset (no heat offset resistance 270.degree. C. .times. 30 min .times. once n = 1) f. Peeling test: passed (sample before and after heat resistance n = 1) g. Melting point: 228.degree. C. h. Hardness(Vickers hardness): 23.0 i. Solder: zero-cross time before heat resistance wettability average 0.85 (sec) after heat resistance average 0.87 (sec) wet strength before heat resistance average 23.0 (mg) after heat resistance average 23.0 (mg) (n =5) j. Bonding: before heat resistance average 1.56 (kg) strength: after heat resistance average 0.56 (kg) (n = 5) k. Plating thickness: average 4.21 (.mu.m) (measured with fluorescent .times. rays n = 9) l. Composition: Sn 97.31% Bi 2.69%(measured at A) "Sn" a. Appearance: passed (free of spot, stain and discoloration) b. Heat resistance: discoloration present (160.degree. C. .times. 6 Hr heat resistance. no expansion, peeling, discoloration and fall-off) c. Solderability test:passed (after heat resistance, 230.degree. C. .times. 3 sec .times. once n = 1) d. Bending test: (after heat resistance, 180.degree. C., bend-back test, measured at A n = 1) e. Melt-originated: no melt-originated offset (no heat offset resistance270.degree. C. .times. 30 min .times. once n = 1) f. Peeling test: passed (sample before and after heat resistance n = 1) g. Melting point: 232.degree. C. h. Hardness (Vickers hardness): 11.40.degree. C. i. Solder: zero-cross time before heatresistance wettability average 0.50 (sec) after heat resistance average 0.61 (sec) wet strength before heat resistance average 31.40 (mg) after heat resistance average 34.20 (mg) (n = 5) j. Bonding: before heat resistance average 1.63 (kg) strength: after heat resistance average 0.70 (kg) (n = 5) k. Plating thickness: average 3.99 (.mu.m) (measured with fluorescent X rays n = 9) l. Composition: Sn 99.84% Bi 0.16% (measured at A) (3) Evaluation Method and Data 1 Hardness (Vickershardness) measuring conditions Measure portion "A" of non-heat-resisted samples under the following conditions by using a super light load minute hardness meter (model mvk-1). a. load: 0.5 fg b. load keeping time: 15 sec c. load speed: 0.01 mm/sec Measure the diagonal line of a dent three times and compute the Vickers hardness from the average dent area. 2 Zero-crossing time, wet strength measuring conditions Five portions "A" of samples S of a frame were sampled from one piece shown in FIG.1 and were measured under the following conditions using a solder checker (SAT-2000). a. Sn 60%, Pb 40% b. TEMP 230.degree. C., SPEED 25 mm/sec c. DEPTH 2m, SENS 1 d. Flux present (MI L type R used)

(4) Solder Wettability Data

1 The solder wettability data of Sn--Ag is illustrated in Table 5.

TABLE 5 Sn--Ag Data Average Zero-cross before 0.65 0.69 0.63 0.67 0.60 0.65 heat resistance (sec) after heat 1.02 0.90 0.80 1.00 1.05 0.95 resistance Wet strength before 84.0 69.0 81.0 55.0 68.0 71.4 heat resistance (mg) after heat 32.023.0 27.0 20.0 30.0 26.4 resistance

2 The solder wettability data of Sn--Bi is illustrated in Table 6.

TABLE 6 Sn--Bi Data Average Zero-cross before 1.01 0.82 0.97 0.62 0.83 0.85 heat resistance (sec) after heat 0.76 0.85 0.99 0.89 0.88 0.87 resistance Wet strength before 16.0 24.0 19.0 35.0 21.0 23.0 heat resistance (mg) after heat 25.022.0 24.0 20.0 24.0 23.0 resistance

3 The solder wettability data of Sn is illustrated in Table 7.

TABLE 7 Sn Data Average Zero-cross before 0.49 0.49 0.34 0.54 0.64 0.50 heat resistance (sec) after heat 0.73 0.49 0.61 0.59 0.63 0.61 resistance Wet strength before 27.0 34.0 44.0 28.0 24.0 31.4 heat resistance (mg) after heat 28.0 41.032.0 37.0 33.0 34.2 resistance

(5) Bonding Strength Measuring Conditions

Cut portion "C" under leads at 3 mm in width, and sample ten from two pieces. Place cut samples one on another with a clearance of 0.3 mm and solder-dip-under the following conditions using a solder checker. a. Sn 60%, Pb 40% b. TEMP230.degree. C., SPEED 25 mm/sec c. DEPTH 2mm, SENS 1 d. Flux present (MI L type R used)

Measure the force to peeling by using a push-pull gauge.

TABLE 8 Sn--Ag Data Average Sample before heat 0.38 0.29 0.53 0.37 0.28 0.37 resistance Sample after heat 0.03 0.07 0.08 0.02 0.05 0.05 resistance

TABLE 9 Sn--Bi Data Average Sample before heat 1.30 1.54 1.23 1.52 2.21 1.56 resistance Sample after heat 0.53 0.35 0.74 0.54 0.65 0.56 resistance

TABLE 10 Sn--Bi Data Average Sample before heat 1.32 1.82 1.62 1.57 1.83 1.63 resistance Sample after heat 0.57 0.62 0.60 1.01 0.69 0.70 resistance

(6) Plating Thickness Measuring Portion

Three portions "A", "a" and "b" of a sample S of a frame per piece were measured and as there were five pieces of frames, a total of nine portions, both ends and the center, were measured using fluorescent X rays.

TABLE 11 Left end Average Sn-Ag of frame Center Right end (.mu.m) Measuring 3.99 4.04 4.10 portion A a 3.85 3.97 4.05 b 4.07 4.21 4.03 4.03

TABLE 12 Left end Average Sn-Bi of frame Center Right end (.mu.m) Measuring 4.29 3.95 3.75 portion A a 4.08 4.31 4.27 b 4.47 4.54 4.21 4.21

TABLE 13 Left end Average Sn-Bi of frame Center Right end (.mu.m) Measuring 4.53 3.79 3.70 portion A B 4.27 3.83 3.95 C 3.99 3.94 3.89 3.99

(7) Measuring Portions

As shown in FIG. 1, the measuring portions "A" and "B" of the sample S of the frame may indicate other portions of the same shapes in one piece. That is, it means that they include the measuring portion "A" and portions "aa" and "b" or the like.

With regard to the evaluation coats, evaluation method and measuring method, the results of the comparison of the characteristics of the individual Pb-free coats as shown in Tables 14to 16 were obtained.

TABLE 14 Evaluation coats Composition Names (Remainder: Sn) Note Sn-Ag Ag 3.0-5.0% Sn-Bi Bi 1.0-3.0% Sn-special Bi 0.1-0.5% Sn coat for surface waveform plating mount As-special Pb 5.0-15.0% Solder coat (As waveform plating bathed) forsurface mount BF-special Pb 5.0-15.0% Solder coat (boron waveform plating fluoride bathed) for surface mount Glossy solder Pb 5.0-15.0% Ordinary glossy solder plated coat (coat for connector or the like) Glossless solder Pb 5.0-15.0% Ordinaryglossless solder plated coat (outer solder coat)

TABLE 15 Evaluation method Evaluation items Contents Appearance Free of spot, stain and discoloration Heat resistance heat resistance at 150.degree. C. .times. 3 Hr, no expansion, peeling, discoloration and fall-off Solderability230.degree. C. .times. 3 sec .times. once after heat resistance. Solder should be 95% or more after soaking Bending 180.degree. C. after heat resistance. No plating separation in bend-back test Melt test No coat offset when non-heat- resistedproduct is heated at 270.degree. C. .times. 30 min and cooled and condensed Peeling Cut a sample after heat resistance with a cutter, apply a cellophane tape and remove it, and plating should not be peeled

TABLE 16 Evaluation method Evaluation items Contents Melting Measured temperature at end of point (.degree. C.) melting using METTLER FP900 thermo system Solder Measured five times under the wettability following conditions using zero- cross time, wet strength measuring conditions, solder checker (SAT- 2000). Sn 605, Pb 40%, TEMP 230.degree. C., SPEED 25 mm/sec, DEPTH 2 mm flux present "zero-cross (sec) wet strength (mg)" samples before and after heat resistance n = 5 Vickershardness Mesured non-heat-resisted samples under the following conditions by using a super light load minute hardness meter (model mvk-l). load: 0.5 gf, load keeping time: 15 sec, load speed: 0.01 mm. Measured the diagonal line of a dent three times and computed the Vickers hardness from the average dent area Bonding strength Sampled ten samples at a width of 3 (kg) mm. Place cut samples one on another with a clearance of 0.3 mm and solder-dip them under the following conditions using asolder checker. sn 60%, Pb 40%, EMP 230.degree. C., SPEED 25 mm/sec. DEPTH 2 mm. Flux present. Measured force to separation using a push-pull gauge. Samples before and after heat resistance n = 3 Plating thickness Measured with a fluorescent X-ray (.mu.m) film thickness measuring unit Composition (%) Pb-less plating . . . Measured by SEM Pb-less So (Scannig Electron Microscope). N = 3 So plating . . . Measured with a fluorescent X-ray film thickness measuring unit. N = 5.

EXAMPLES

Examples of this invention will now be described with reference to the accompanying drawings. In the diagrams, "1" is a lead frame where a mount component, such as an IC chip, is mounted, and which has an island portion 2 in the center portionand a plurality of outer leads at the periphery.

"3" denotes outer leads which become to-be-plated portions and protrude outward of the IC package, and "4" is a ball lead portion which becomes a to-be-plated portion as external leads of CSP.

While alloy plating to be applied to the aforementioned. to-be-plated portions contains Sn and a plating material other than lead, and the composition is as follows. The set ratios are Bi=1.0% with respect to Sn=99.0% in the first example, andBi=2.0 to 10.0% with respect to Sn=9.80 to 90.0% in the second example. The ratio is set to Ag=1.0 to 3.0% with respect to Sn=99.0 to 97.0% in the third example. The ratio is set to Ag=3.0 to 5.0% with respect to Sn=97.0 to 95.0% in the fourth example. The ratio is set to Ag=8.0 to 10.0% with respect to Sn=92.0 to 90.0% in the fifth example. The ratio is set to Cu=0.5 to 1.0% with respect to Sn=99.5 to 90.0% in the sixth example.

"5" is an-IC chip, a mount component, to be mounted on the lead frame 1, "5'" is an LSI chip, and "5"" is a chip tantalum capacitor. "6" denotes inner leads, and "7" is a package which has the IC chip 5 or the LSI chip 5' molded with a resin. FIG. 8 shows an IC wafer.

In FIG. 6, "8" is an IC wafer in a pretreatment in the IC fabrication process, and a plurality of patterns are formed on the IC wafer of 150 to 200 mm in diameter.

Specific Examples of Steps

(1) IC Fabrication Process a. IC wafer step=form a plurality of patterns on the IC wafer (FIG. 6) of 150 to 200 mm in diameter. There are actually over 300 steps to this step. b. Dicing=dice the IC wafer 8 into individual semiconductor IC chips5 (FIG. 6). The above are pretreatments. c. Die bonding=adhere and fix the IC chip 5 to the island portion 1' of the lead frame 1 (FIG. 7). d. Wire bonding=bond the IC chip 5 to electrodes 3' of the lead frame 1 and the inner leads 6 (FIG. 7). e.Resin mold=perform resin molding to form and protect the package 7 (FIG. 8). The above are post-treatments.

(2) IC Assembling Step a. IC lead frame forming=form the elongated lead frame 1 by press punching and photoetching a rolled thin metal plate (42 alloy, copper alloy) (chain-line portion in FIG. 6). b. Inner plating=apply gold plating or silverplating to the IC lead frame (island portion 2 and inner leads 6) before resin molding (FIG. 6). c. Die bonding and wire bonding=bond the IC chip 5 to the island portion 2 of the lead frame. Then, connect the IC chip 5 to the electrodes 3' of the leadframe 1 by the inner leads 6 (FIG. 7). d. Resin molding=Scale and fix the IC chip 5 and the inner leads 6 in the package 7 with plastic, such as epoxy resin or silicon resin (FIG. 8). e. Baking=perform a high-temperature treatment for stabilizationafter resin molding. f. Resin variable removal=remove a thin resin coat sticking out over the lead frame 1 at the time of resin molding. Thereafter, perform honing with water jet, resin or glass beads. g. Outer plating=Plate the outer leads 3 with aPb-free material according to this invention containing Sn as an essential component and Bi, Ag or Cu by using an electrolytic process with a special waveform with a melting point in a range of 220 to 250.degree. C. That is, as the aforementioned alloyplating material, Bi is set to or less 1.0% with respect to Sn=99.0% in the first example, Bi is set to 2.0 to 10.0% with respect to Sn=98.0 to 90.0% in the second example, Ag is set to 1.0 to 3.0% with respect to Sn=99.0 to 97.0% in the third example,Ag is set to 3.0, to 5.0% with respect to Sn=97.0 to 95.0% in the fourth example, Ag is set to 8.0 to 10.0% with respect to Sn=92.0 to 90.0% in the fifth example, and Cu is set to 0.5 to 1.0% with respect to Sn=99.5 to 90.0% in the sixth example. h.Cutting=cut away the individual IC packages 7 from the linked frames (chain lines K in FIG. 8, chain lines K in FIG. 5). i. Bend the outer leads 3 according to the intended mounting (FIG. 2 shows mounting on a printed circuit board). j. Mount the ICpackage 7 on an electrode pattern 10 of a printed circuit board 9 and solder bonding portions to the outer leads 3 (FIGS. 2 and 3). In this case, it is placed on the electrode pattern 10 of the printed circuit board 9 that faces the ball leads 4 of BGAor CSP (FIG. 4).

Effect of the Invention

With the above-described structure, this invention eliminates Pb from a solder material as a bonding material which is essential for electronic components in the production of electronic devices, thereby preventing a possible pollution problemsuch that when electronic devices which become unnecessary are disposed of, Pb leaks and seeps into groundwater.

In mounting electronic components, alloy plating equivalent to or greater than Pb can be acquired without using Pb but by using other bonding materials than Pb.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1]

FIG. 1 is a plan view of one piece of a frame 1.

[FIG. 2]

FIG. 2 is a perspective view of an IC package that packages an IC chip to which alloy plating is applied with a substitute bonding material for Pb according to this invention is mounted on a lead frame.

[FIG. 3]

FIG. 3 is a cross-sectional view of an IC package to which alloy plating is applied with a substitute bonding material for Pb according to this invention and which is mounted on a printed circuit board.

[FIG. 4]

FIG. 4 is a cross-sectional view of an LSI package to which alloy plating is applied with a substitute bonding material for Pb according to this invention and which is mounted on a printed circuit board.

[FIG. 5]

FIG. 5 is a plan view of a chip tantalum capacitor mounted on a lead frame.

[FIG. 6]

FIG. 6 is a perspective view of dicing and die bonding in the IC fabrication process.

[FIG. 7]

FIG. 7 is a perspective view of wire bonding in the IC fabrication process.

[FIG. 8]

FIG. 8 is a perspective view of packaging a lead frame with resin molding.

DESCRIPTION OF REFERENCE NUMERALS A first measuring portion B second measuring portion a third measuring portion b fourth measuring portion 1 lead frame 2 island portion 3 outer leads 4 ball lead portion 5 IC chip 6 inner leads 7 IC package 8 ICwafer 9 printed circuit board 10 electrode pattern 11 soldering bonding portion

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